1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for isolating and testing one or more sections of pipeline.
2. Description of the Related Art
Once a pipeline is constructed, the pipeline must undergo pressure testing to ensure integrity before put into operation. The pressure test often includes a leak test and a strength test. The section of pipeline to be tested can vary in length, such as between 10 and 50 km, depending on the terrain, locations of pipeline access, and many other factors. Several tests can be performed, section by section, until the integrity of the entire pipeline has been proven.
Current pressure testing procedures use special high pressure test headers that are welded on to each end of the pipeline test section. The pipeline section is then filled with a pressure test medium which can be a liquid or gas. Depending on the diameter of the pipeline and the length of the section(s) to be tested, the volume within the pipeline to be filled with the pressure test medium can be immense.
On large diameter pipes the normal practice is to use water due to the high power demands of compressing large volumes of a gas. In such case, a water source must be found, such as a river or lake, and the water must be delivered to the test header location. Often times the project requires construction of a dedicated water delivery pipeline to meet the required volumetric flow rates. After the pipeline is filled with water, specialized equipment is needed to “squeeze”, or pressurize, the line up to the test pressure. Some codes require the pipeline to be pressured up to 125% of the expected operating pressure. The pressure is held for a certain amount of time (usually 4 to 24 hours). If a pressure loss is detected, the leak must be found and repaired, and the entire section must be re-tested. If the pipeline test section is long, locating the leak can be very difficult and time consuming, especially if the pipe is buried.
In freezing conditions, the water may require freeze-depressant additives. The volume of these freeze-depressant additives can often reach 50% of the total test volume, thus requiring the purchase and delivery of large volumes of expensive chemicals. Further, environmental concerns arise due to the presence of the chemicals, especially when a leak may release harmful substances to the environment.
An alternative to using freeze-depressant chemicals is to use large heat exchangers to add thermal energy to the water. The heaters would add enough energy to the water to prevent freezing during the entire time span of the hydrotest. This option can also be very expensive. To achieve uniform temperature distribution across the entire length of the test section, the water is heated and circulated, from entry to exit, several times. This may require heating 5 to 10 times the actual pipe section volume, Heating these volumes of water will consume a large quantity of diesel, thus further increasing power consumption and fuel delivery costs. Additional background can be found in U.S. Pat. No. 6,339,953 to Ashworth, U.S. Pat. No. 4,872,336 to Ballie, U.S. Pat. No. 6,467,336 to Gotowik, DE 297 14 238 U1 to JT-Elektronik GMBH, U.S. Pat. No. 4,429,720 to Beck et al., and EP 0 147 648 A to BBC Aktiengesellschaft Brown, Boveri & Cie.
There is a need, therefore, for a tool and method for pressure testing a pipeline that require a smaller test volume, reduce the need and/or quantity of freeze-depressant additives, and reduce power consumption.